Flame resistant fabrics are those fabrics made from flame resistant fibers, also known as FR fibers, and blends of flame resistant fibers. Some flame resistant fabrics may also include a minority of non-FR fibers that are blended with flame resistant fibers. Flame resistant fibers, or FR fibers, are those fibers that have flame resistance as an essential characteristic of the fiber. Flame resistant fibers could be inherently flame resistant fibers or fibers treated to become flame resistant. Typically, a treated fiber is a conventional textile fiber that has been treated with a flame retardant, or a chemical substance used to impart flame resistance. Not only can the fiber be treated with a flame retardant, but the resulting fabric can also be treated with a flame retardant to make the fabric flame resistant. For example, treated fibers or fabrics include: FR cotton, FR-treated rayon (both FR cellulosics), and the like. Inherently flame resistant fibers may include: aramids, polyamide imides, melamines, polybenzimidazole (PBI), polyimides, polyphenylene benzodisoxazole (PBO), polyphenylene sulfide (PPS), carbon, Polytetrafluoroethylene (PTFE), polyetherether ketone (PEEK), modacrylic, inherently-FR rayon, liquid crystal polymers, and the like.
Most often these flame resistant fibers (treated and/or inherent) are blended together to obtain a yarn for a fabric with a particular blend of preferred properties. The preferred properties include thermal protection, static resistance, comfort, durability, stability, appearance, moisture management, abrasion resistance, anti-bacterial, ease of laundry maintenance, color, relative cost, etc., and combinations thereof. As a result, flame resistant fabrics can be used for many different purposes and in many different industries. These include, but are not limited to, the fire service industry, military, law enforcement, wildland fires, urban search and rescue incidents, in foundries, at electrical utilities, in the chemical, oil, gas, and petrochemical industries, in auto racing, areas of rioting, and illicit drug manufacturing labs, just to mention a few. One specific example of a use for a flame resistant fabric is the outer shell fabric of a firefighter's personal protective garment used in structural fires, also known as the outer shell fabric for fireman's turnout gear.
With such a broad range of application, it should be understood that there exists a need for flame resistant fabrics in many different colors and shades of colors. Typically, flame resistant fibers and fabrics are provided in various colors and shades by dyeing the fabric or yarn, also known as piece-dyeing or yarn-dyeing. For example, a process of piece-dyeing or yarn-dyeing a PBI fiber to a black color is to add a dye to the fabric after it is produced or to add a dye to the yarn after it is produced. One problem with traditional piece-dyed or yarn-dyed flame resistant fabrics is sublimation of the dyes from the fabric due to high heat exposure, flame exposure, and fading due to long-term excessive UV exposure, or the like. For example, a traditionally yarn-dyed black PBI/para-aramid flame resistant fabric when exposed to significant heat may cause the fabric to change to a reddish brown color in the area of heat exposure. As another example, a traditionally piece-dyed black PBI/para-aramid flame resistant fabric when exposed to significant heat exposure can cause the fabric to change to a similar reddish brown color in the area of the heat exposure. This overall color change of the fabric is clearly not desirable.
Another way to produce a colored flame resistant fabric is to utilize solution-dyed fibers. Solution-dyeing, also known as dope-dyeing or producer-dyeing, is a process where a colorant is added to the chemical compound before extrusion of the fiber. There are numerous known means of producing solution-dyed fibers. It has been found that flame resistant fabrics constructed of solution-dyed flame resistant fibers retain their color far better than piece-dyed or yarn-dyed fabrics after significant heat exposure, flame exposure, long-term overexposure to UV light, etc., or any other factors which may fade color of piece-dyed or yarn-dyed fabrics. Keeping with the previous examples, a black PBI/para-aramid fabric that is solution dyed has held far more of its black color than the yarn-dyed or piece-dyed PBI/para-aramid fabric examples discussed above and does not turn to the reddish brown color when exposed to high heat. This minimal color change is clearly an advantage over the piece-dyed and yarn-dyed fabrics. However, because of the minimal color change, one of the problems discovered with solution dyed flame resistant fabrics is that they do not indicate when the fabric has been exposed to any significant heat exposure, flame exposure, long-term overexposure to UV light, etc., as with the piece-dyed and yarn-dyed fabrics. As a result, the solution dyed flame resistant fabrics do not indicate when the garment and its components need to be evaluated for further damages.
The instant invention is designed to solve the problem with both piece-dyed/yarn-dyed flame resistant fabrics and solution dyed flame resistant fabrics by providing a way to keep the positive attribute of a fabric made of solution-dyed fibers, (minimal overall color change, i.e., maximum colorfastness) while still providing some sort of indicator to the end-user that the garment had seen a high heat exposure, flame exposure, excessive UV light exposure, or other factors which may fade color of piece-dyed and yarn-dyed fibers.
The instant invention of a flame resistant fabric with tracing yarns is designed to address the above mentioned problems.